Department of Neurobiology and Genetics, Institut de Génétique et de Biologie Moléculaire et Cellulaire, CNRS UMR_7104, Inserm U 964, Université de Strasbourg, Illkirch, France.
J Neurochem. 2011 Feb;116(3):350-62. doi: 10.1111/j.1471-4159.2010.07114.x. Epub 2010 Dec 13.
Lateral interactions at the first retinal synapse have been initially proposed to involve GABA by transporter-mediated release from horizontal cells, onto GABA(A) receptors expressed on cone photoreceptor terminals and/or bipolar cell dendrites. However, in the mammalian retina, horizontal cells do not seem to contain GABA systematically or to express membrane GABA transporters. We here report that mouse retinal horizontal cells express GAD65 and/or GAD67 mRNA, and were weakly but consistently immunostained for GAD65/67. While GABA was readily detected after intracardiac perfusion, it was lost during classical preparation for histology or electrophysiology. It could not be restored by incubation in a GABA-containing medium, confirming the absence of membrane GABA transporters in these cells. However, GABA was synthesized de novo from glutamate or glutamine, upon addition of pyridoxal 5'-phosphate, a cofactor of GAD65/67. Mouse horizontal cells are thus atypical GABAergic neurons, with no functional GABA uptake, but a glutamate and/or glutamine transport system allowing GABA synthesis, probably depending physiologically from glutamate released by photoreceptors. Our results suggest that the role of GABA in lateral inhibition may have been underestimated, at least in mammals, and that tissue pre-incubation with glutamine and pyridoxal 5'-phosphate should yield a more precise estimate of outer retinal processing.
在最初的研究中，人们认为水平细胞通过谷氨酸盐转运体将 GABA 释放到表达于视锥细胞末梢和/或双极细胞树突上的 GABA(A) 受体，从而介导了第一级视网膜突触的侧抑制作用。然而，在哺乳动物的视网膜中，水平细胞似乎并没有系统性地包含 GABA，也不表达 GABA 膜转运体。在这里，我们报告称，小鼠视网膜水平细胞表达 GAD65 和/或 GAD67 mRNA，并可微弱但持续地被 GAD65/67 免疫染色。尽管心脏内灌流后很容易检测到 GABA，但在经典的组织学或电生理学准备过程中，GABA 会丢失。将其置于含有 GABA 的培养基中孵育并不能恢复 GABA，这证实了这些细胞中不存在 GABA 膜转运体。然而，当添加吡哆醛 5'-磷酸（GAD65/67 的辅助因子）时，GABA 可以从谷氨酸或谷氨酰胺从头合成。因此，小鼠水平细胞是一种非典型的 GABA 能神经元，没有功能性 GABA 摄取，但具有谷氨酸盐和/或谷氨酰胺转运系统，允许 GABA 合成，这可能依赖于光感受器释放的谷氨酸盐。我们的研究结果表明，GABA 在侧抑制中的作用可能被低估了，至少在哺乳动物中是这样，并且在组织预孵育时添加谷氨酰胺和吡哆醛 5'-磷酸，应该可以更准确地估计外视网膜的处理过程。
